The Investigation Of Structural Phase Transitions And Dielectric Properties In Divalent Metal-Hexacyanocobaltate(?) Based Host-Guest Compounds

Dielectric transition materials are a type of responsive dielectric materials with dielectric constant switching between high-and low-dielectric states upon external stimuli.They can find applications in fields such as switching,sensing and recognition.Host-guest compounds are good candidates to show dielectric transition behaviors due to order-disorder transitions of the guests which are located in the well-matched host cages.Double-perovskite metal-hexacyanocobaltate(?)frameworks A2[B'Co(CN)6](A ?cationic organic guest;B'= monovalent metal ion)have intriguing host-guest type structures,phase transitions and dielectric transition behaviors.In this study,the B' ion is replaced by four different divalent metal ions,i.e.,Cd(?),Mg(?),Ca(?)and Sr(?).Fifteen divalent metal-hexacyanocobaltate(?)based host-guest frameworks were synthesized:A2?H(CdCl2)[Co(CN)6]}(A = protonated imidazolium(1);pyrazolium(2);guanidinium(3);protonated thiourea(4)),(C4N2H14)2{(H2O)2(Cd3Cl4)[Co(CN)6]}(5),(SCN2H4)(SCN2H5){(H2O)3Mg[Co(CN)6]}(6),(C3N2H5){(H2O)5Mg[Co(CN)6]}(7),(CN3H6){(H2O)4Mg[Co(CN)6]}(8),B{Ca[Co(CN)6]}(B = C(NH2)3(9);OCN2H5(10):SCN2H5(11)),(C4NOH10){Ca[Co(CN)6]}(12),(C2H6NH2){(H2O)4Ca[Co(CN)6]}(13)),(MA)(H20)[Sr(H20)2Co(CN)6](14)and(MA)[SrCo(CN)6](15).Among them,1,3,4,6,9,10,11 and 14 undergo reversible structural phase transitions and dielectric transition behaviors,being potential switchable dielectric materials.In particular,14 shows dually thermo-and chemo-triggered dielectric transitions and moister-based dielectric sensing.The research demonstrates that,owing to the diverse and labile coordination modes of the divalent metal ions,the metal-hexacyanocobaltate(III)based host-guest frameworks can possess rich structures,phase transitions and dielectric transition behaviors.These results provide good starting materials and ideas for future application study.